Error when calling function that returns HTML within email template

Question

Context

I generated a standard email template via the IDE. Since I want to dynamically build an HTML table within the email, I added a function that takes a list and returns HTML. However, calling it from within the email's main [hsx|...|] results in the error:

Couldn't match type ‘context’ with ‘ControllerContext’
        arising from a functional dependency between constraints:
          ‘?context::ControllerContext’
            arising from a use of ‘renderList’ at Admin/Mail/Accounts/Report.hs:(16,35)-(47,6)
          ‘?context::context’
            arising from the type signature for:
                           IHP.MailPrelude.html :: forall context.
                                                   (?context::context, ConfigProvider context) =>
...

The function returning Html itself compiles fine, but calling it from within the instance's [hsx|...|] results in a compiler error. The called function can have no arguments and the result is the same. What triggers it is when the function returns Html. String or Text is fine.

Using IHP Pro 1.0.0.

Example

module Admin.Mail.Static.Test where
import Admin.View.Prelude
import IHP.MailPrelude

data TestMail = TestMail { user :: User }

instance BuildMail TestMail where
    subject = "Subject"
    to TestMail { .. } = Address { addressName = Just "Firstname Lastname", addressEmail = "[email protected]" }
    from = "[email protected]"
    html TestMail { .. } = [hsx|
        Hello World
        {renderFoo}
    |]

renderFoo :: Html
renderFoo = [hsx|foo|]

Question

I can use functions to generate snippets of HTML in other (non-email) views with no problem so why does it not work here?